A few months ago I wrote to this forum because we were having difficulty getting through to the Twitter support team to resolve an issue where it was blocking hashtags from sending in Tweets.
It was very frustrating at the time, as there was no specific guidance.
However with the help of Andy Piper someone in the support team did follow up with us.
If Twitter is blocking hashtags from sending from your app, we have found that the advice to turn off all hashtagged Tweets, and ensure that best practices suggested by Twitter support are followed, the tags will begin to work again.
Thank you very much.